In a convoy travel of multiple vehicles forming an organized group of vehicles, following vehicles (i.e., “followers”) in a convoy, which follow a leader vehicle (i.e., a “leader”), respectively receive travel information directly from the leader vehicle for performing vehicle travel control and organizing a convoy. Such a technique is disclosed in, for example, Japanese Patent Laid-Open No. 2009-239585 (JP '585). According to such technique, the following vehicles other than an immediate following vehicle (i.e., a right behind vehicle) of the leader vehicle are also enabled to perform the travel control that quickly reflects the travel information of the leader vehicle.
When multiple following vehicles in the convoy respectively perform a vehicle travel control by directly receiving the travel information from the leader vehicle in the convoy, the following vehicles must stably receive high quality travel information of the leader vehicle. Therefore, the information transmitted by the leader vehicle of the convoy at a time of convoy travel of the vehicles may include information regarding the number of vehicles in the convoy (i.e., capacity information of the convoy, which indicates the current allowable number of vehicles that can be included in a convoy).
The capacity information may include the number of vehicles either as (i) actual numbers, i.e., the maximum number and the current number of the vehicles in the convoy, or as (ii) a calculated number, i.e., a difference between (ii-a) the current allowable number of vehicles that can be included in a convoy based on the communication capacity of a wireless communication unit in the leader vehicle and (ii-b) the currently-included number of vehicles currently included in the convoy.
By having the leader vehicle transmit information including the convoy capacity, the number of vehicles in the convoy is kept within a certain limit for allowing all convoy vehicles to stably receive the transmitted information from the leader vehicle. That is, in such manner, each vehicle in the convoy can securely receive the information from the leader vehicle.
However, even when the capacity information indicates that the convoy capacity still allows a new vehicle to join the convoy, the new vehicle may not be able to join the convoy in some cases. That is, for example, when one or more of the following vehicles already in the convoy are a large-size vehicle and such large-size vehicle blocks, or interrupts, the electric wave from the leader vehicle, the new vehicle cannot join the convoy.
In such case, because of the blockage/interruption of the electric wave from the leader vehicle by such large-size vehicle, the new vehicle cannot receive convoy travel information from the leader vehicle, thereby not allowed to join the convoy.